Guven, what did you do before errors appeared?
If your site is not live:
1. Delete current "Video" plugin
2. Download new one from Store.
3. Install new plugin
Note: you will lose all videos when deleting the plugin.
If your site is a live one and you can't delete the plugin
1. Roll back any changes you did before the error appeared.
2. Check ow_base_component table of your database. Does it have VIDEO_CMP_UserVideoListWidget ?